Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
PHN 8115
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The invention relates to a pick-up arm
suitable for an apparatus for mPchanically scanning grooved
rotary discs~ such as phonograph records, with the aid of an - -
electrical pick-up, and comprising a shank which is at least
,i 5 partly made of a composite material consisting of high strength
thin fibres embedded in a matrix; a head at one end of the
shank for mounting and protection of the pick-up and provided
with electrical connection means for the pick-up; a bearing
block near the shank end which is remote from the head and pro- -~
vided with bearing means; bearing means connected to the shank
which co-operate with those of the bearing block and electrical
conductors extending from the head to the bearing block for
transferring electrical signals from the pick-up to an elect-
; ~ ronic amplifier to be connected to the pick-up arm.
A pick-up arm manufactured from a composite
material is known from German Offenlegungsschrift 2,432,974
and 2,435,191. In comparison with the conventional pick-up arms,
for example those which are provided with an aluminium shank,
such pick-up arms have the advantage that the arms can be made ?.`
substantially lighter at the same rigidity or even appreciably
higher rigidity. Many composite materials, for example those
which consist of graphite fibres embedded in a matrix o~ epoxy
resin, have a ratio between the madulus of elasticity and
density which is substantially greater than that of the usual
materials. For example, in the case of aluminium of a quality
which is suitable for pick-up arms the said ratio is
2.67 x 108 cm, whereas for a composite material consisting of
60% graphite fibres in an epoxy matrix this can be 11.8 x lo8 cm.
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PHN. 8115.
In acldition, composite materials may exhibit very great strength,
whilst they m~y also have other properties which are attractive
for pick-up arms, such as a lc~ coe fficient of thermal expansion,
good internal c~mping, and being nonrmagnetic. For further
information with respect to the aclvantage of such pick-up armEi,
reference is made to the tw~ afore-nentioned Offenlegungsschriften.
Referen oe is also macle to them ~or the m~nufacturing method. In
this respect it is merely mentioned that for example the shank may
be manufactured starting frc~ flat thin plates or sheets, consist-
ing of adjaoe ntly arranged carbon fibres which are joined to each
other by means of an epoxy resin. From these sheets a sleeve-
shaped shank can be formed, which is plaoe d in a mould and heated
therein at approximately 170C. Heating causes the epoxy resin
to melt, thus forming a matrix in which thie carb3n fibres are
embedded. After remDval frc~ the mDuld and a second heat treat-
ment a thin tube of a camposite material is thus c~btainecl.
In the pick-up arms kncwn until now the elec-
trical conductors which extend between the pick-up and the
bearing block are formed by 3 or mDre copper wires prcwided wi~h a
plastic insulating sheath. me core thickness of these wires is
typically 0.3 mm. In high quality pick-up arms the wires are
stranded in order to minimize cr~ss-talk between the different
audio channels and also for reasons of manufacturing technology.
mis is because during assembly the strand can be handled m~re
simply thian a number of separate wires.
A drawback of these known arms is that the
electrical conductors have a oQmparatively high self-capacitance
and fur~h=rnore the wei~ht of the stranded wires is typically
approxImately 1 gram. For use in a pick-up arm of a composite
PHN 8115
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material this would correspond to approximately one third of
the weight of the actual arm, which may be of the order of 3
grams. A further drawback is that fitting the stranded wires
into the shank of the pick-up arm is difficult.
It is an object of the invention to avoid
the drawbacks outlined above especially with pick-up arms manu-
factured of a composite material of the type mentioned in the
~ preamble. In a pick-up arm according to the invention the
-` electrical conductors are embedded in the composite material
of the pick-up arm.
- Embedding electrical conductors in a pick-up
arm is known per se, for example from British Patent Specific-
ation 1,339,042. This concerns a pick-up arm for a toy phono-
graph1 which pick-up arm is integrally manufactured of a ther-
moplastic material, the vertical and horizontal movements of `
the pick-up arm being possible by the provision of locally thin
portions in the pick-up arm material, which portions serve as
integral hinges. In such a pick-up arm the electrical conductors
must be capable of withstanding the movements at the location of
the hinges. As a result of this, comparatively thick electrical
wires must be used. However, if no hinges were formed in the
thermoplastic material, the electrical conductors would still
have to be comparatively thick in view of the high elasticity
of the plastic used for the pick-up arm and the low dimensional
stability thereof. Embedding the electrical conductors in a
pick-up arm of composite material including high strength fibres
has the special advantage that in view of the previously ment-
ioned very high rigidity of the composite material very thin
electrical conductors may be used. This provides great improve
ment in that the electrical conductors have only a small in-
fluence on the mass of the arm and the conductors have a low
PHN 8115
ZS~
self-capacitance.
An embodiment of the invention is character-
~ ized in that each of the electrical conductors consists of a
; solid metal wire. In conventional pick-up arms such conductors
cannot be used because they are liable to break. Pick-up arms
of a composite material, however, are so rigid that embedded
wires in the form of solid metal wire with a metal cross-section
of approximately 20 microns may be used. Such thin wi~es cannot
be used in convent;onal pick-up arms.
In pick-up arms of the type mentioned in the
preamble and in which the composite material contains electric-
ally conductive fibres such as carbon fibres, it is advantageous
to use an embodiment of the invention which is characterized -
s in that each of the conductors consists of a wire with a solid
metal core which is surrounded by an enamel sheath are used on
a large scale in electrical technology, for example in the
manufacture of coils. In a pick-up arm in accordance with the
invention they constitute for the first time a material which
is suitable for wiring high-quality pick-up arms. `
Preferably an embodiment is used which is
characterized in that the electrical conductors are embedded
at mutually equal distances. This step contributes to a low
self-capacitance of the wires. An optimum result can be ob-
tained with an embodiment in which the conductors are embedded
at the outer surface of the composite material. This embodi~
ment moreover has obvious advantages in respect of production
technology, owing to the fact that the electrical conductors
need not be fitted until at a final stage.
In a further preferred embodiment, to pro-
vide electrical shielding and also for esthetic improvement,
the shank is provided
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P~N. 8115.
with a thin ~rotective metallic layer. The shank may for example
be surrounded by a thin met~l foil which is glued on it. Another
possibility is that the protective layer consists of a metal layer
deposited on the oQmposite material. At present many processes -'
'5 æe kncwn to those skilled in the art, in accordance with which
metal layers can be deposited on plastic components with the aid
of a sult~ble process, for example by immersion in a bath.
Pick-up arms in accordance with the invention
may be of extremely light construction and therefore, also in
view of their other previously mentioned favourable properties,
they are emunently suitable for use in record players of very
high quality, such as hi-fi record players and quadraphonic
record players. Pick-ups may be used which bear on the record
with a force s~aller than 1 gram. It will be evident that with
such pick-up-arms the pick-up æm is readily susceptible to
undesired torques. Such torques might for exa~ple be exertsd
on the arm at the location of the bearing block. The pick-up
arm is pivoted`to the'bearing block, so as to allow the pick-up
arm to perform vertical pivotal movements. Near the bearing
block the electrical aonductors must therefore be led out of
the pick-up arm and oonnected'to connecting means provided out-
side the pick-up arm. These connectlng means should have a
minimal influence on the'pick-up arm move~ents and should exert
minimal counteracting torques'on said arm. meréfore, it is
advantageous to employ an enbcdiment of the ~nvention which is
characterized in that the bearing means which are connected to
the shank consist of bearing journals which are integral with
the shank and which are also made of ccmposite material, and
that the conductors are embedded in at least a part of the
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. PHN.8115
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~ bearing journals. Since the forces exerted on the conductors act
; at a very small radius, only small torques which counteract the
pivotal arm movements are produced. Pref`erably, the bearing
block is also made of cornposite material and provided with em-
5 bedded electrical conductors. In particular in conjunctiorl with
the pick-up arms described herein.before this has the advantage
that very small counteracting torques are exerted on the pivotal
movements oP the bearing block by the electrical conductorsO
~; As the bearing block i9 of a composite material it is again pos-
: ... 10 sible to use very thin conductors, ~rhich are moreover station-
, . . arily arranged in the mat-e-rial and can consequently transfer
the eleotrical signals from the bearing arrangement to a location
- underneath a record player deck without exerting undesired
torques on the bearing block.
In particular ~rhen very thin electrical con-
,,. . ductors are used an embodin1ent is of importance which i9 cha-
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. racterized in that the shank and/or the bearing block is provided
with metal connecting elements for electrically connecting the
conductors to each other and also to the electronic amplifj.er5
which elements are embedded in the oomposite material, pro~ject
. partly therefrom and are rigid in oomparison with.the eleotrical
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cond~ctors. ~i-s metal connecting elements may consist o~
j.
soldering tags or pins or other suitable components.
The invention will be described i.n more de-
tail with reference to the drawing which schematically sho~r.s an
embodiment and in ~rhich:
- Fig. 1 is a perspective view of a pick-up
arm in accordance with the invention7 in which for the sake o-.f
clarity a metal screening cap at the location of the bearing
block has been rai.sed and a part o:~ a bearing support has bcen
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PHN 8115
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broken away at the location of one of the bearlngs,
Fig. 2 is a cross-section of the shank of
the pick-up arm of Fig. 1,
Fig. 3 is a cross-section at the location of
the bearing block,
Fig. 4 is a scaled-up exploded view, in per-
spective, at the location of one of the bearing supports o~ the
pick-up arm of Fig. 1, and
Fig. 5 is a scaled-up side view at the loc-
ation of the pick-up arm of Fig. 1.
In Fig. 1 the pick-up arm bears the general
reference numeral 1, and the pick-up mounted on it has the re-
ference numeral 2. The pick-up arm comprises a shank 3 of a
composite material and has connected thereto a head 4 for mount-
ing and protection of a pick-up. In the head two threaded holes
`~ are formed which bear no re~erence numerals in the Figure and
in which fixing bolts 5 are fitted for securing the pick-up to
the head in known manner ;n accordance with the RETMA (Radio,
Electronics and Television Manufacturers Association) standard.
Near the shank end which is remote from the head a bearing block
is located which bears the general reference numeral 6. The -
bearing block is provided with two bearing elements or bushings
7, only one of them being visible in Fig. 1 and also in Fig. 4.
Said bearing bushings cooperate with bearing iournals 8 and 8'
which are connected to the shank. From the head four conductors
9 run towards the bearing block 6 for transferring the elect- -
rical signals from the pick-up 2 to an electronic amplifier, not
shown, to be connected to the pick-up arm. The electrical wires
are embedded in the composite mat~rial of the pick-up arm and com-
prise a solid copper wire 10, which is surrounded by an enamel
insulating sheath 11. For this see in particular Fig. 2, which
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PHN 8715
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also clearly shows that the electrical conductors are embedded
at the outer surface of the composite material at mutually equal
distances. At its outer surface the shank 1 is provided with a
thin metallic protective layer in the form of a metal foil 12
which is glued on it.
As previously stated, the bearing means which
` are connected to the shank 1 comprise two bearing journals 8
which are integrated with the shank and which consequently also
consist of composite material. In eacn of the bearing journals 8
and 8' two of the four electrical conductors are embedded. The
bearing block 6 is also made of composite material and is pro-
vided with electrical conductors 13 which correspond to the con-
ductors 9 of the shank. The bearing block 6 comprises a flange- -
, shaped portion 14 and two bearing supports 15 and 15' disposed
at either side of the shank 1. In these bearing supports slots
16 and 16' are formed which are open at one end and which have
a width which is slightly greater than the diameter of the cor-
responding bearing journals 8 and 8'. Opposite their open ends -:
the slots terminate in openings 17 of greater diameter, see Fig.
4. The bearing element or bushing 7 comprises a cylindrical
portion 18 and a flange 19 at the end thereof. The diameter of
the cylindrical portion 18 corresponds to the diameter of the
opening 17. During assembly the bearing journals 8 are fitted
in the openings 17 of the bearing supports 15 via the slots 16,
after which the plain bearings 7 are fitted onto the bearing
journals and are cemented in position in the bearing block with
a small amount of glue. The bearing block 6 is pivotally mounted
in a mounting flange 21 by a number of balls 20. A retaining
ring 35 engages a portion 22 of the bearing block which extends
further downwards to retain the block in the flange 21. This
portion is located underneath
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' the record player deck when the pick-up arm mDunting flange 21 is
m~unted on a record player. In the fully assembled condition
the bearing supports 15 are 03vered by means of a pr~tective
metal cap 23. Slots 24 and 24' are formed'at tw3 sides in this
cap. The slot 24 serves for the passage of the part of the shank
1 which faces the'head 4, and the slot 24' for the part of the
shank 1 which faces the other side, around which part, as is com~
man practice, a mDvable counterweight 25 is mounted for balancing
the pick-up arm.
- 10 Both the shank and the bearing block æe pro-
- vided with metal oonnecting elements or electrical ter~inals
which are rigid in oc ~ arison with the electrical conductors,
which are embedded in the'composite material and which partly
project therefr~m, for electrically connecting the conductors to
each other and to the'electronic a~plifier to be connected. At
' the location of the head 4 in Fig. 4 only tw~ such oonnecting
', elements are shcwn in the form of tw~ soldering pins 26 and 26'.
To each of these pins, four such pins bein~ provided in total,
one of the oonductors 9 is oonnected, namely inside the material
of the'head 4, see in particular Fig. 5. The portions of these
pins which project from the'head 4 are oonnected to pins 29'and
' 29' of the'pick~up 2 by means of wires, bearing the reference
numerals 27 and 27' in Fig. 5, and with the aid of associated
oonnectors 28 and 28'. Although Fig. 5 shows only tw~ pins 29
and 29' of the pick-up, it is obvious that in reality four pins
are providecl, in acoordance with the number of o~nductors in
the arm 1. m e journal 8 is provided with 2 soldering pins 30 '
and 31, the bearing support 15 with tw~ soldering terminals or
tags 32 and 32' and the cylindrical portion 22 of the bearing block
with four soldering terminals or tags 33, 33', 33" and 33"'. me ~ -
soldering pins 30 and 31
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as well RS the correspond:ing soldering pins, not shown, in the
journal 8', are connected to the electrical conductor 9, whilst
the solderlng tags 32 and 32 ? of the bearing su~port 15, as well
r c, i~ fer~:on n cc 7~e, c/
. as the correspollding soldering tags 33 and 33 ? /by means of
5 electrical conductors 13. The connection ~rom the solderirJg
tags 32 and 32' to the soldering pins 30 and 31 are formed by
very th~n ~l~xible wires 34 and 341.
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